[GreenKeys] [External] PP-3054/UG

[Jones, Douglas W]

From: W2HX [w2hx at w2hx.com] -- Monday, November 20, 2023 6:53 PM

> The manual (thanks, Nick) says it uses a constant voltage transformer. My experience is that these can hum quite loudly. Can anyone confirm my suspicion on these?

I googled the manual, which shows the usual setup I'm familiar with for ferroresonant transformer voltage regulators.  The ones I've worked on are in 1960s vintage PDP-8 computers, which relied on such tranformers for voltage regulation -- without the benefit of the zener diodes used in the PP-3054/UG.  The ones I worked with hummed quietly, no annoying noise level.  I suspect that the fact that the chassis was aluminum might matter here.  A steel chassis might hum louder because it's attracted to stray fields around the transformer.

In any case, the big risk with ferroresonant transformers is the capacitor.  The original capacitors are paper-foil capacitors (in a can) saturated with PCB oil.  When they fail, they tend to explode with a cloud of unpleasant PCB smoke.  In the PDP-8 restoration world, the general advice is, replace the capacitor now, don't wait for the explosion.  I've followed this advice.  Modern replacement capacitors tend to use polyester film instead of oil soaked paper, packaged in the usual can.

           Doug Jones